The invention relates to an apparatus and a method for filling an open container, preferably an open bag.
In order to accurately weigh a product, it is common to split the product flow into a coarse stream and a fine stream. A worm may hereby be used for example as dosing member. This type of product feed is provided exclusively for realizing a high weight accuracy.
The net system involves in some cases a separation of the product flow into fine and coarse streams when being filled into the scale, whereas the gross system involves a separation during filling the container.
In general, the gross system provides only little productivity which is disadvantageous. At the same time, there is no possibility to compact the product during the weighing phase because any type of manipulation has an impact on a weight.
Gross systems are also known which provide an intermediate compaction at a non-critical weighing moment during the weighing and filling processes.
Cited as prior art are U.S. Pat. No. 3,209,844 A, DE 36 40 520 A1, U.S. Pat. No. 3,404,742 A, CH 683 251 A5, DE 38 11 880 A1, U.S. Pat. No. 3,589,411 A, GB 1 011 653 A, DE 101 32 715 C1, CH 611 216 A5, U.S. Pat. No. 4,275,775A, and GB 661 224 A.
U.S. Pat. No. 3,209,844 describes a filling device with a scale by which a coarse weight is pre-metered (underweight) which is then fully emptied into the filling container. Subsequently, a volume dosing wheel supplies a fine stream.
DE 36 40 520 describes a filling device to first weigh the quantity to be filled and then to discharge it directly into a bag.
U.S. Pat. No. 3,404,742 describes a weighing device by which a coarse stream of the filling material is volumetrically pre-metered and released in a scale receiver. Doses of the fine stream are then added. Subsequently, the total filling material portion is dispensed.
CH 683 251 A5 uses a differential scale as weighing device and dispenses the released product directly from the scale as coarse and fine streams.
DE 38 11 880 A1 deals with the problem of maintaining the filling material continuously under vacuum during an otherwise known filling procedure in order to prevent contamination as a result of environmental impacts.
U.S. Pat. No. 3,589,411 describes a filling apparatus having two separate connections into a bag to be filled. Each of the connections has its own weighing mechanism for alternatingly weighing the material. A feeder with an impeller that rotates at constant revolution compacts the product so that the material to be filled drops pre-compacted in accordance with the revolving compartments into a filling container. The impeller thus assumes the function of ventilation and compaction of the filling material. (Continuous transport as a result of product compaction).
All afore-mentioned apparatuses lack basically apparatuses for product compaction or are dimensioned for only little output.
Powdery products which are also very fine have the characteristic of intake of air during transport and also during the filling operation, leading to a significant increase in volume. As a consequence, the bags normally used for packaging must have a respectively great volume to provide enough space for the product in the bags.
After the product has again released the air entirely or partly following the filling of the bags, for example through introducing compaction measures or after elapse of a certain time, the product takes up a respectively smaller volume, so that the bag or the bag article becomes too big, i.e. packaging material is given away, resulting in higher costs and problems when stacking the bags. The afore-mentioned prior art is unsuitable to overcome these problems satisfactorily.